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World Expression

World Expression is a point object, which executes arbitrary expressions (scripts) within the specified distance and at a set frame rate. By default, expressions are executed at the same frame rate as the main application.

Notice
An expression is executed only if it's within the specified distance from the camera.

By using World Expression, you can attach a script to an object in the scene. To do that, such object must be added as a child node to World Expression. Child nodes inherit transformations (if any) of the World Expression node.

Notice
Child nodes are transformed relative to the pivot point of the World Expression node.

If there are nested World Expression nodes, the child node of the last World Expression in the hierarchy inherits transformations of all parent World Expression nodes.

For example, by using World Expression, you can transform objects in the scene, turn on and off sounds with the distance, turn on and off NPC behavior, attach objects to the camera (e.g. drops of the rain on the camera), and so on.

Mesh Dynamic nodes added as children to the nested World Expression nodes

See also#

Creating World Expression#

To create World Expression via UnigineEditor:

  1. On the Menu bar, click Create -> Logic -> Expression.

  2. Place the World Expression somewhere in the world.

Attaching World Expression Script#

There are two ways of attaching a World Expression script via UnigineEditor:

  • Directly in UnigineEditor in the Source field of the World Expression section in the Parameters window. Source code must be inside the curly braces {}, as they define the World Expression scope.

  • Attached as a script file in the File field of the World Expression section. The script file should be included in the World Expression scope in the Source field using the curly braces {}:

    In this case, the my_expression.h file should contain the following code:

    Source code (UnigineScript)
    log.message("WorldExpression is updated\n");
    Notice
    In the script file, the source code must not be wrapped in the curly braces {}.

Implementing Script#

The script itself can be implemented as a simple sequence of functions' calls or as a set of functions and classes. See examples here.

Notice
It is recommended to implement simple scripts.

Inter-Script Communication#

Such script can communicate with the world script via the corresponding engine.world class functions or with World Trigger via callbacks (see the samples listed above).

Script Functions#

Besides functions of the UnigineScript library, there is also a set of internal functions that are available within the World Expression script. The list of such functions with descriptions and examples can be found here.

Setting World Expression Parameters#

You can adjust the following parameters of World Expression in the Node tab:

Update Distance Limit Distance from the camera, within which the expression is executed.
IFps A constant frame duration (inverse FPS, 1/FPS) used to execute the expression. If 0 is set, the expression is executed at the same frame rate as the main application.
File

A path to a file with a World Expression script to be executed. The path is relative to the data directory. This file should be included in the World Expression scope in the Source field. This field is optional as the World Expression script can be implemented directly via the UnigineEditor interface.

Notice
If the script file is changed, it should be refreshed via UnigineEditor: click to the right of the File field.
Source

Source code of a World Expression script. This field can contain:

  • Direct implementation of the World Expression script
  • The #include directive that loads the script file specified in the File field.
Notice
In both cases, the curly braces {} must wrap the code in the field.
Last update: 2021-05-26
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